The present invention relates to drilling apparatus and more particularly to latch mechanism for releasably retaining a core barrel inner tube assembly, plug bit drilling assembly and similar apparatus in a drill string in an earth formation.
In U.S. Pat. No. 2,905,438 to Church the spearpoint has the one ends of a pair of links pivotally connected thereto, the opposite ends of said links being pivotally connected to the mid-portions of the latches. The one ends of each latch is pivotally connected to the core barrel cap, the upper ends of the latches being movable into a latch seat of a drill string.
U.S. Pat. No. 1,364,254 to Currier discloses an overshot assembly for withdrawing an article through the drill string and having a pair of plates with hanger straps secured thereto and extending thereabove, a jaw pivot extended through axial slots in plate slots, a pair of grappling jaw members pivotally mounted by the jaw pivot with the jaw pivot being axially between the jaws and the upper end of the jaw members, a pair of links having their remote ends pivotally connected to the upper end of the respective jaw member and adjacent ends pivotally connected by a link pivot and a clevis having the link pivot extend therethrough for having a cable or rod secured thereto to retract the clevis. The link pivot is axially movable in slots in the upper ends of hanger straps and is moved upwardly to result in the jaw members moving to a gripping position.
U.S. Pat. No. 3,340,939 to Lindelof discloses a core barrel inner tube assembly having a pin mounted to a latch release tube to move therewith and move into a slot formed by the latches when the latches have moved to their latch seated position for retaining the latches in a latch seated position until a retracting force is applied to the latch release tube. U.S. Pat. No. 4,800,969 to Thompson discloses a latching arrangement similar to Lindelof, other than it does not refer to the pin retaining the latches in a latch seated position.
With core barrel inner tube assemblies such as disclosed in Lindelof and Thomson wherein the latches in their latch seated position are of an axially outwardly opening "V" shape and are retracted by outward movement of the their latch release tubes, the initial axial outward movement of the spearpoint acts to force the latches more tightly against the drill string latch seat shoulder. As a result in, for example, a core blockage situation resulting in the latch body forcing the latches against the latch seat, the pulling force exerted on the spearpoint forces the latches more firmly against the latch seat. This makes it difficult, if possible, to retract the core barrel inner tube assembly through the use of an overshot assembly. For example the pulling force required to be exerted on the latch release tube to retract the latches may be so great that the wire line cable breaks before the latches are moved out of abutting relationship to the latch seat, and thus the core barrel inner tube assembly remains in its latched condition in the drill string with the overshot assembly coupled thereto and part of the broken cable falling downwardly in drill string.
In order to make improvements in latching mechanism for drilling apparatus that includes, for example, wire line core barrel tube assemblies, retractable drag bits and earth sampling tubes that are retractable through a drill string and/or an outer barrel, this invention has been made.